In recent years, in a field of taking an image of a subject for medical use, industrial use or the like, particularly, in a field of an electronic endoscope, there is known an apparatus of taking a tomographic image of a subject by using a method of OCT (optical coherence tomography).
According to the tomographic apparatus by OCT, light is used as a detecting probe and therefore, there is not posed a problem that a subject is exposed to X-ray irradiation as in an X-ray imaging apparatus of a related art, and the apparatus is extremely preferable particularly when the subject is the human body. Further, a large-sized apparatus of CT, MRI or the like is not needed, the subject can simply be inspected and therefore, a burden of the subject in view of cost or a burden in view of a physical strength thereof can be alleviated and the apparatus is preferable also in this respect.
Further, according to the tomographic apparatus using OCT, by utilizing low coherence of light having a spectrum width in a wide band, interference wave information at respective positions in a depth direction of the subject is provided and therefore, reflected light from an inner portion of the subject can be detected by a spatial resolution of μm order, and a measurement resolution can considerably be promoted in comparison with that of the X-ray imaging apparatus of the background art.
The tomographic apparatus using OCT having a number of excellent characteristics in this way is disclosed in, for example, Optics vol. 32, No. 4 (2003): Manabu Sato, Naohiro Tanno. Further, there is specifically proposed a tomographic apparatus using OCT which is technically devised variously (refer to, for example, JP-A-2003-329577 or the like).
However, it is a current state that an apparatus which is satisfactory in a speed of acquiring image information with regard to a subject, an amount of information thereof or the like has not been necessarily proposed and reduced into practice and a further improvement has been desired.
Particularly, when an optical tomographic apparatus is used for medical use, it is necessary to make a physical or spiritual burden on a subject in accordance with inspection as small as possible and for that purpose, there is desired an apparatus capable of acquiring a tomographic image with regard to a number of affected portions by a number of times of irradiation as small as possible.